Draft National Wind Farm Development Guidelines - July 2010

The near field zone can be calculated, and is dependent upon the frequency of the
signal, the gain and orientation of the antenna.
Typical calculations give the “near-field” zone for:
High Band Ultra High Frequency (UHF) signals, such as cellular telephones
(800MHz to 1900MHz) as approximately 20m.
For point-to-point Microwave links as approximately 720m.
For Low Band VHF paging systems approximately 4m.
As can be seen from the above examples the near-field zone varies widely
depending upon the service type. It is recommended that a conservative criterion for
discussing potential impact due to near-field effects with a potentially affected party
is if the wind farm proponent intends to locate a wind turbine within, say, 1km of any
telecommunications site.
• Reflection/scattering
This occurs when Radio signals are reflected (scattered) from the wind turbine blades
and interfere with a wanted radiocommunications signal.
A ratio of the scattered signal to the received signal can be used to determine the full
effect of this form of interference. This can be calculated and is dependent upon the
distance of the receiver and transmitter to the wind turbine tower. Some methods use
worst-case Radar Cross Section (RCS), which is very conservative, or a variant on the
second Fresnel zone calculation for users close to a wind turbine. Please note that
RCS is relevant to all radiocommunications services, not just radar services.
Required signal-to-noise ratio (SNR) for different services is variable, but can be of the
order of 30dB.
An exclusion zone to meet the SNR requirement can be calculated and is dependent
upon the gain and radiation pattern of the antenna, the worst case RCS and the
distances between user, transmission tower and wind turbine. Higher frequency signals
generally utilise antenna patterns with higher gain.
As there is no single criterion for potential impact on radiocommunications services
due to scattering, it is recommended that the criterion for discussing potential impact
due to reflections/scattering with a potentially affected party is if the wind farm
proponent intends to locate a wind turbine within 2km of any telecommunications
site.
Consultation with the organisations listed earlier in this section will reveal any effects
on radar services.
In summary, the recommended criteria for discussions with a potentially affected party are,
if the wind farm proponent intends to locate a wind turbine:
• Within the maximum second Fresnel zone of a point-to-point radio link.
• Within 2km of a radiocommunications site or a receiver.
• Within 250 nmiles of Aeronautical and Weather Radar operations.
It should also be noted that the accuracy of radiocommunications site coordinates in the
ACMA database is variable, and also that it relies upon the accuracy of individuals
providing the correct data when applying for a new service. It also does not guarantee
that a particular service is operating, or operating in accordance with ACMA regulations.
Therefore, should there be an indication that any individual services may be impacted, or
are within, say, 5 km of causing an impact, then it is recommended that independent
verification of the radiocommunications site co-ordinates is carried out to confirm the
existence of any issues.
Page 176 Draft National Wind Farm Development Guidelines – 2 July 2010